Our research focuses on the structure and function of apolipoprotein (apo) E and other proteins involved in heart and Alzheimer's diseases. Our main structural tool is x-ray crystallography. In order to increase our efficiency in solving new structures and avoiding the needto use multiple isomorphous replacement to solve the phase problem, we have developed recombinant protein expression systems with which seleno-methionine can be substituted for methionine. With this substitution we can phase directly on a single crystal using the technique of multiple anomalous dispersion (MAD). We propose to use the UCSF Mass Spectrometry Facility to confirm the incorporation of seleno-methionine into our recombinant proteins before proceeding with crystallization and data collection, which will be done at a MAD station at a synchrotron facility.